1. Field of the Invention
This invention relates to variable function devices and particularly although not exclusively to variable counter-balance devices for use in T.V. or video camera pan and tilt heads for controlling tilt movement of the head.
2. Description of the Prior Art
U.S. Pat. No. 4,447,033 (Sachtler GmbH Filmtechniche Gerate) discloses a mechanism or support for a television or movie camera which allows the camera to be tilted or pitched upwardly and downwardly. The weight or torque applied by the camera when tilted from its neutral position is counterbalanced by means of a series of accumulators or spring elements placed between a rotor of the camera support camera and a stator portion of the support. The elements are adapted to be selectively engaged between the rotor and stator depending on the weight of the camera being used. Each accumulator offers a restoring torque that is different from that of the other accumulators such that by selective engagement of various combinations of accumulators, many different weights of cameras can be accommodated.
Individual accumulators are locked with the staters by means of a central operating handle which is rotatably located over the cylindrical stator and has on its inner periphery several cams. These cams serve to press lock pins into recesses of the respective accumulators when the handle is rotated.
By a planned placement of cams on the inner surface of the central operating handle, one or more lock pins can be selectively engaged with their respective individual accumulators by appropriate positioning of the handle. In order to achieve all possible combinations of accumulators it is necessary to be able to re-select accumulators at different positions of the movement of the handle and whilst two or four positions of engagement can be accommodated, difficulties arise in providing eight or more positions which may be necessary to maximise the number of combinations possible from a given set of accumulators.
This invention provides a system for performing a variable function comprising a plurality of selectively operable devices which provide a required function, actuator means for selecting/deselecting devices over a range of movement of the actuator means, the actuator means including stepped drives for selecting/deselecting at least one of the devices at a predetermined ratio with respect to another of the devices whereby devices can be selected to operate individually or in combination by movement of the actuator means to provide multiple levels of the function.
Preferably the actuator means comprise at least 35 two rotary shafts each having means for selecting/deselecting one or more devices with rotation of the shafts, and drive means coupling the shafts in a predetermined drive ratio whereby the devices are selected singly or in possible combination to provide a range of accumulated functions from the devices.
More specifically the drive ratio between the shafts maybe 2:1.
In one embodiment according to the invention the drive between the shafts may comprise a belt drive extending around wheels of different diameters on the shafts to provide the required drive ratio.
In any of the above arrangements at least one of the actuator drives may have a plurality of devices associated with the drive for selection/deselection.
More specifically drives may select and deselect a plurality of devices.
Further, said stepped drive is preferably arranged to select said devices singly and in all possible combinations through its cycle of movement.
In any of the above arrangements the respective 20 devices may provide progressively increasing functional.
For example the functional effect provided by respective devices may increase in a progression by a factor of two from the lowest function to the highest function.
In one particular application of the invention the function provided by the devices may be a torque resistance to rotation to provide counter-balance in a mechanism for use in a tiltable camera mounting system.